The principal objective of this work is to understand in as much detail as possible the mechanisms whereby Zn/Cu, Fe, and Mn containing superoxide dismutases catalyze the reaction 2O2 plus 2H yields H2O2 plus O2. Our procedures involve the application of a variety of physical techniques ranging from X-ray crystallography to obtain three dimensional structures to spectroscopic measurements to characterize the electronic structures of the various metallo proteins. The kinetic mechanisms will be explored using a stopped-flow spectrophotometer specially designed for the study of superoxide in aqueous media. The methodology of studying enzymes at sub-zero temperatures will be applied in studying the mechanisms of superoxide dismutases.